1. Field of the Invention
The present invention relates to a thin-film magnetic write head, such as a floating type magnetic head, and to a method of fabricating the same. More particularly, the invention relates to a thin-film magnetic write head suitable for track narrowing that writes data onto a recording medium as reliably-readable signals for a magnetic read head and to a method of fabricating the same.
2. Description of the Related Art
A thin-film magnetic head has an inductive head and a magnetoresistive (MR) head. The thin film magnetic head may be mounted in a hard disk drive and the like. The inductive head is for writing signals onto a recording medium, such as a hard disk. The MR head for reading signals from the recording medium.
In general, an inductive head includes a lower core layer composed of a magnetic material, an upper core layer which is opposed to the lower core layer with a nonmagnetic gap layer therebetween at a surface facing a recording medium, and a coil layer for inducing a recording magnetic field in the core layers. Magnetic signals are written onto the recording medium by means of a fringing magnetic field between both core layers.
With increasing recording density, there is a need to cope with the narrowing of the track by decreasing the track width Tw of the inductive head. The track width Tw is determined by the width of the edge of the upper core layer that is exposed at a surface facing the recording mediumxe2x80x94the air-bearing surface (hereinafter xe2x80x9cABSxe2x80x9d).
For example, conventionally, the upper core layer is formed by a frame plating method. In the frame plating method, a resist layer patterned in the shape of the upper core layer is formed. The interior of the pattern is then plated with a magnetic material for forming the upper core layer. By removing the resist layer, an upper core layer with an edge having a width corresponding to the track width Tw is obtained.
However, in the frame plating method, it is very difficult to pattern the resist layer with a minute track width Tw because the resolution of exposure has limitations when the resist layer is patterned. As the recording density further increases, this problem becomes more noticeable.
Japanese Unexamined Patent Application Publication No. 7-296328 (hereinafter xe2x80x9cUNEXAMINED APPLICATIONxe2x80x9d) discloses a structure of an inductive head formed by another frame plating method and a method of fabricating the same. FIG. 10 is an enlarged partial front view of the periphery of a core of the inductive head which is formed by the frame plating method disclosed in the UNEXAMINED APPLICATION.
As shown in FIG. 10, a notch structure 120 composed of silicon dioxide or the like is formed on a lower pole layer (lower core layer) 102. FIG. 11 is a perspective view, which shows the shape of the notch structure 120. The notch structure 120 is provided with a trench 148. A pole tip layer P1(T), a gap layer G, and a pole tip layer P2(T) are formed by plating in the trench 148.
A pole tip 108 of an upper pole layer (upper core layer) having a larger width than that of the pole tip layer P2(T) is formed on the pole tip layer P2(T) and the notch structure 120.
The UNEXAMINED APPLICATION describes a thin-film magnetic write head having a submicron track width can be provided. The UNEXAMINED APPLICATION further describes the prevention of magnetic saturation associated with narrowing of a track by the formation of the pole tip 108 having a larger width than that of the pole tip layer P2(T), as shown in FIG. 10.
In the method described in the UNEXAMINED APPLICATION, the pole tip layer P1(T), the gap layer G, and the pole tip layer P2(T) are formed in the trench 148 by electroplating using a direct current. However, if the inner width of the trench 148 is set at 1 xcexcm or less in order to provide a thin-film magnetic write head having a submicron track width. the surface of the pole tip layer P1(T) is curved as shown in FIG. 12. Consequently, the surface of the gap layer G deposited on the pole tip layer P1(T) is also curved.
As shown in FIG. 13, if the surface of the gap layer G is curved with respect to a recording track on a recording medium in which data are recorded by the thin-film magnetic write head, a boundary B for reversal of magnetization on the recording track is curved in the direction of motion of the magnetic track (X direction).
If the boundary B is curved, it is difficult to read the data with high definition. When a read head H is in the vicinity of the boundary B as shown in FIG. 13, both ends of the read head H and the central section of the read head H are located in reversed magnetization regions R+ and Rxe2x88x92, respectively. The magnetization regions have different magnetization directions. As a result, the read outputs cancel each other out.
The surface of the pole tip layer P1(T) is curved because it is difficult to obtain uniform current distribution in the trench 148 during plating when the inner width of the trench 148 is 1 xcexcm or less. Conventionally, when plating is performed in the trench 148, electroplating is performed using a direct current.
When electroplating is performed using a direct current, if the current density is decreased to less than 30 mA/cm2, the current distribution in the trench 148 becomes nonuniform. In particular, the pole tip layer P1(T) is curved, and consequently, the gap layer G is also curved.
Even increasing the current density during electroplating so the current distribution in the trench becomes uniform is of no avail. If the current density is increased to more than 30 mA/cm2 when electroplating is performed using a direct current, xe2x80x9cburnt depositsxe2x80x9d occur. The plating surface becomes turbid and rough, instead of being bright and uniform. Thus the quality of the gap layer G is degraded.
Accordingly, it is an object of the present invention to provide a thin-film magnetic write head in which the curvature of the surface of a gap layer is reduced even if a track width is 1 xcexcm or less, and in which data can be written onto a recording medium as signals reliably readable by a magnetic read head. A further object is to provide a method of fabricating the thin film magnetic write head.
In one aspect of the present invention, a thin-film magnetic write head includes a lower core layer and an upper core layer with a nonmagnetic gap layer therebetween at a surface facing the recording medium (ABS). The lower core layer is composed of a magnetic material. The upper core layer is composed of a magnetic material that is opposed to the lower core layer. The thin-film magnetic write head writes data to be read by a thin-film magnetic read head having a track width Tr and a distance H2 between an upper shielding layer and a lower shielding layer. A length in the track width direction (track width) at a magnetic contact between the gap layer and the upper core layer is 1 xcexcm or less. The formula Axe2x89xa6H1xe2x88x92H2 is satisfied. A is a difference between the height of the upper surface of the gap layer on a center line in the track width direction and the height of the upper surface of the gap layer at a distance Tr/2 from the center line in the track width direction. H1 is a gap length of the gap layer. H2 is the distance between the upper and lower shielding layers.
It is preferable that the surface of the gap layer of the thin-film magnetic write head is completely planar. However, in practice, a curvature is allowed to a certain extent depending on the size of the thin-film magnetic read head. The formula Axe2x89xa6H1xe2x88x92H2 defines a tolerance for the curvature of the gap layer. FIG. 1 is a schematic diagram illustrating the formula Axe2x89xa6H1xe2x88x92H2.
The thin-film magnetic write head writes data into the recording medium while reversing magnetization directions. The recording track for recording data is shaped like a band in which reversed magnetization regions R+ and reversed magnetization regions Rxe2x88x92, which have opposite magnetization directions, are alternately placed, as shown in FIG. 13. A width W of the reversed magnetization region R+ or Rxe2x88x92in the track moving direction (X direction) varies depending on the content of the data to be recorded. In theory a minimum value of W is equal to the gap length H1 of the gap layer of the thin-film magnetic write head. Therefore, the shape of a reversed magnetization region having the minimum width W and the frontal shape of the gap layer are identical to each other.
FIG. 1 shows a state in which the thin-film magnetic read head scans a reversed magnetization region R1. The width W corresponds to the minimum value H1 among the reversed magnetization regions R+ and Rxe2x88x92. H2 represents a distance between the upper shielding layer and the lower shielding layer of the thin-film magnetic read head. In FIG. 1, the track width Tr of the thin-film magnetic read head is equal to the width of a section for reading a magnetic field in the thin-film magnetic read head. Examples of the section for reading the magnetic field include magnetoresistive elements, such as a GMR (giant magnetoresistive) element and an AMR (anistropic magnetoresistive) element.
A curvature of the gap layer of the thin-film magnetic write head is allowable as long as region M lies within the reversed magnetization region R, on the recording track. Region M has a width corresponding to the width of the section for reading the magnetic field in the thin-film magnetic read head (i.e., the track width Tr) and a length corresponding to the distance H2 between the upper shielding layer and the lower shielding layer of the thin-film magnetic read head. When a bottom Mb of the region M overlies a bottom R1b of the reversed magnetization region R1, a corner Ma1 of a top Ma of the region M should not exceed a top R1a of the reversed magnetization region R1.
The above can be formulated in that A must be smaller than a difference between the gap length H1 and the thickness H2 of the region M. A is a difference between the height of the upper surface of the gap layer on a center line C and the height of the upper surface of the gap layer at a distance Tr/2 from the center line C in the track width direction.
FIG. 1 shows a state in which the equation Axe2x89xa6H1xe2x88x92H2 is satisfied. In FIG. 1, when the bottom Mb of the region M overlies the bottom R1b of the reversed magnetization region R1, the corner Ma1 of the top Ma of the region M lies on the top R1a of the reversed magnetization region R1. If the gap layer is more curved than the state shown in FIG. 1, the value A increases, resulting in A greater than H1xe2x88x92H2. The corner Ma1 of the top Ma of the region M would exceed the top R1a of the reversed magnetization region R1.
If the formula Axe2x89xa6H1xe2x88x92H2 is satisfied, the curvature of the gap layer is reduced so that the region M lies within the range of the reversed magnetization region R1 on the recording track. The magnetic read head can read the signals recorded on the reversed magnetization region R1 reliably and clearly.
In the present invention, the curvature of the gap layer of the thin-film magnetic write head can be confined within a practically allowable range. Even when the thin-film magnetic write head is formed with a track width of 1 xcexcm or less, data are recorded on the recording medium as signals which are reliably read by the magnetic read head.
In the present invention, preferably, the gap layer is composed of at least one nonmagnetic metallic material selected from the group consisting of NiP, NiPd, NiPt, NiRh, NiW, NiMo, Au, Pt, Rh, Pd, Ru, Cr, Ag, and Cu.
In the present invention, to facilitate the narrowing of the track width, the thin-film magnetic write head preferably includes a lower core layer, an insulating layer, a lower pole layer, a gap layer, an upper pole layer, and an upper core layer. The insulating layer is formed on the lower core layer. The insulating layer has a trench with an inner width corresponding to the track width. The trench extends from the surface facing the recording medium (ABS) in the height direction. The lower pole layer is formed on the lower core layer in the trench. The gap layer is formed on the lower pole layer in the trench. The upper pole layer formed on the gap layer in the trench. The upper core layer is in magnetic contact with the upper pole layer.
Another aspect of the present invention, provides a method of fabricating a thin-film magnetic write head having a lower core layer composed of a magnetic material, and an upper core layer composed of a magnetic material that is opposed to the lower core layer, and a gap layer therebetween at a surface facing a recording medium (ABS). The method includes: forming the lower core layer by plating; forming an insulating layer on the lower core layer, the insulating layer having a trench with an inner width corresponding to a track width, the trench extending from the surface facing the recording medium in the height direction; of forming a lower pole layer by plating on the lower core layer in the trench; forming the gap layer by plating using a nonmagnetic metallic material on the lower pole layer in the trench; forming an upper pole layer by plating on the gap layer in the trench; and forming the upper core layer by plating on the upper pole layer, the upper core layer being magnetically in contact with the upper pole layer. At least the forming of the lower pole layer is performed by electroplating using a pulsed current. The forming of any or all of the lower and upper core layers and the upper and lower pole layers may also be performed by electroplating using a pulsed current.
In the present invention, since at least the formation of the lower pole layer by plating, is performed by electroplating using a pulsed current, the total supply of charge can be reduced while increasing the maximum value of the supply of charge (electric current) per second when the lower pole layer is formed due to plating. Therefore, the present invention provides a current with an intensity sufficient to produce a uniform current density during plating and avoid burnt deposits due to plating.
Consequently, in accordance with the present invention, the lower pole layer and the gap layer can be formed with reduced curvature of the surfaces and with high quality.
Additionally, the formation of the gap layer by plating may be performed either by electroplating using a pulsed current or electroplating using a direct current.
However, to avoid switching from one apparatus to another and provide other manufacturing benefits the formation of the gap layer, the upper pole layer, and the formation of the lower core layer and the upper and lower core layers may be performed by electroplating using a pulsed current.
The present invention is particularly effective when the insulating layer forms a trench with an inner width of 1 xcexcm or less.
If the inner width of the trench is 1 xcexcm or less, the current distribution in the trench easily becomes nonuniform. It is very difficult to prevent the surface of the lower pole layer from curving when plating is performed using a small direct current so as not to produce burnt deposits.
When the lower pole layer is formed by plating using a pulsed current as in the present invention, it is possible to reduce the total supply of charge while increasing the maximum value of the supply of charge (electric current) per second.
With the present invention, even if the inner width of the trench is 1 xcexcm or less, it is easy to maintain uniform current distribution in the trench and to prevent burnt deposits from occurring. The lower pole layer can be formed with reduced curvature and high quality. The gap layer on the lower pole layer can be formed with reduced curvature.
In accordance with the method of fabricating the thin-film magnetic write head of the present invention, the thin-film magnetic write head is fabricated for writing signals to be read by a thin-film magnetic read head having a track width Tr and a distance H2 between an upper shielding layer and a lower shielding layer. Preferably, the formation of the gap layer is performed so that the formula Axe2x89xa6H1xe2x88x92H2 is satisfied. A is the difference between the height of the upper surface of the gap layer on a center line in the track width direction and the height of the upper surface of the gap layer at a distance Tr/2 from the center line in the track width direction. H1 is a gap length of the gap layer.
A curvature of the gap layer of the thin-film magnetic write head is tolerable as long as the region M in FIG. 1 lies within the reversed magnetization region R1 on the recording track. If the gap layer is formed to satisfy the formula Axe2x89xa6H1xe2x88x92H2, the curvature of the gap layer is confined within the tolerance.
The gap layer may be composed of at least one nonmagnetic metallic material selected from the group consisting of Nip, NiPd, NiPt, NiRh, NiW, NiMo, Au, Pt, Rh, Pd, Ru, Cr, Ag, and Cu.
When any of the upper and lower core layers, gap layer, and upper and lower pole layers are formed by electroplating using a pulsed current, preferably, the current density is set in the range from 30 to 150 mA/cm2.
In the present invention, since at least one of the upper and lower core layers, gap layer, and upper and lower pole layers are formed by electroplating using a pulsed current, the current density can be increased during plating. However, if the current density is too large, burnt deposits may occur. In order to prevent burnt deposits from occurring, the current density is preferably set at 150 mA/cm2 or less. If the current density is too small, the curvature of the surface of the gap layer increases. Therefore the current density is preferably set at 30 mA/cm2 or more. If the current density is less than 30 mA/cm2, magnetic properties are degraded.
When any one of the upper and lower core layers, gap layer, and upper and lower pole layers are formed by electroplating using a pulsed current, preferably, the current-applying period is set in the range from 25 to 500 msec.
If the current-applying period is too long during electroplating, the total supply of charge is increased, resulting in burnt deposits. Therefore, the current-applying period is set at 500 msec or less.
If the current-applying period is too short, the formation by plating may take an excessively long time. Additionally, the magnetic properties of the resulting magnetic layersxe2x80x94the upper and lower core layers and the upper and lower pole layersxe2x80x94are degraded. Therefore, the current-applying period is preferably set at 25 msec or more.
When any one of the upper and lower core layers, gap layer, and upper and lower pole layers are formed by electroplating using a pulsed current, more preferably, the current-applying period is set in the range from 50 to 300 msec.
If the current-applying period is set in the range from 50 to 300 msec, burnt deposits can be avoided and the resulting magnetic layers have satisfactory magnetic properties.
When any one of the upper and lower core layers, gap layer, and upper and lower pole layers are formed by electroplating using a pulsed current, preferably, the duty ratioxe2x80x94the ratio of the ON time to the OFF timexe2x80x94of the pulsed current is set in the range from 1/11 to 1/2.
If the duty ratio of the pulsed current is too large, that is, the quiescent period after the current-applying period is too short, the total supply of charge is increased, resulting in burnt deposits. If the duty ratio is too large, in particular, when the upper and lower core layers and the upper and lower pole layers are performed by electroplating using a pulsed current, the magnetic properties of the resulting magnetic layers are degraded. Therefore, the duty ratio of the pulsed current is preferably set at 1/2 or less.
If the duty ratio is too small, the formation by plating takes an excessively long time, which is impractical. Therefore, the duty ratio is preferably set at 1/11 or more.